When Supreme Court Justice Stephen G. Breyer was robbed in his Caribbean vacation home 10 days ago, the crime was unremarkable except for one fact: A machete-wielding intruder was able to walk right into the residence of one of the highest members of the U.S. government.B

In an era when many top U.S. officials are blanketed in security, Breyer and his colleagues are theB exceptions, freer but also more exposed than theirB counterparts in the executive and legislative branches.

Nowadays, it often seems that anyone who is anyone in Washington has a driver and a gaggle of taciturn protectors. Congressional leaders sweep into restaurants trailed by members of the Capitol Police; top White House advisers have Secret Service agents.

And every president is more heavily encircled than the one before. When President Barack Obama wants to snorkel on his Hawaii vacations, the Secret Service clears the airspace above him, the shoreline in front of him and the water around him. An aide said Obama had even been surrounded by agents in wetsuits as he floated.

However, the nine justices often slip aroundB Washington like ordinary citizens, causing barely a pause at stop signs, parties, supermarkets and houses of worship. It is hard to name many officials with more influence than Justice Anthony M. Kennedy, the court’s perennial swing vote, who may determine the fate of Obama’s health care law this spring. But it is easy to name many officials with far more constant protection.

Court officials do not discuss security arrangements in detail, but according to longtime observers and congressional budget requests, they vary depending on a justice’s location: traveling out of town for a speech, walking around Washington or working inside the heavily fortified court building.

In the capital, the justices are protected mainly by the court’s own small force, said a spokeswoman, Kathy Arberg. When the justices leave Washington, the U.S. Marshals Service takes over, and local police departments help, too.

Protection may be relatively light because justices have worked to preserve their freedom of movement, and the Supreme Court has a lucky history — its members have not met with serious violence. The most recent attack took place nearly three decades ago: An assailant who objected to Supreme Court decisions on pornography and school desegregation punched Justice Byron R. White in the face. (By contrast, federal and state judges have experienced far worse, including assassinations and the murders of family members.)

Like Breyer, Justice Ruth Bader Ginsberg and retired Justice David H. Souter have been victims of everyday crime, committed by people who probably did not recognize them. In 1985, a bullet pierced the living room window of Justice Harry A. Blackmun, but investigators concluded that it had probably been fired at random.

"Based on history, it’s tough to make the case that there should be mandatory protection," said Robert Fein, a forensic psychologist who conducted a Secret Service study of assassins and near-attackers.

Over the years, the justices have cited security to support their longstanding objections to broadcasting the court’s oral arguments. (In keeping with tradition, only the few hundred observers who can crowd into the courtroom will be able to witness the proceedings over the national health care law next month. A C-Span video request is pending, though likely to be denied.)

The justices have many reasons for avoiding the cameras, including not wanting their courtroom statements turned into television sound bites, several longtime court observers said. But Justice Clarence Thomas has told lawmakers in Congress specifically that he fears that broadcasting oral arguments could put him and his colleagues in greater jeopardy, and security experts say he is probably correct.

"The fact that they maintain low profiles helps to maintain their overall security," said Marisa Randazzo of Sigma Threat Management, who has consulted on protection for government officials. Television coverage "can really increase someone’s grievance or fixation, especially if we’re dealing with someone who may not be mentally stable," she said.

Still, the justices are not the remote figures of the past. Today, they give frequent speeches at law schools and bar associations, and they have appeared widely on television, from C-SpanB to a cameo this month by Justice Sonia Sotomayor on "Sesame Street."

Such appearances undercut the case against televised proceedings, in the view of Dennis J. Hutchinson, a professor at the University of Chicago Law School and a historian of the court. "They’re all over the place," he said.

Some justices have delighted in their near anonymity. Retired Justice John Paul Stevens cherished one particular encounter, said Richard Davis, a professor of political science at Brigham Young University. One day, Stevens was walking outside the court when tourists stopped him. They wanted to know if he would mind moving out of the way so they could take a good photograph of the Supreme Court.